Why/when to use switched power supply?

[ltg]

Hi,

Could someone please explain for me when or why to use switched power supply? Is it cheaper compare to traditionally power supply? Or does it take small place on pcb board?
Is there any tum rules when to use switched power supply?

Thanks in advance!
Best Regards,
ltg

 

[jochez]

It use less power so it can be made smaler!!!
And for batery application it will be usefull...

 

[FANT]

Switching power supply

Here following you will find some pros and contra about the switching power supply:

Pro:
1) Usually the efficency of a power supply is at least 70 % with any load ( except open, of course ) instead in a traditional power supply ( with transformer ) the efficency is related to the load;
2) The power factor of a switching P.S. can be made in between 0,9 and 1 , with good results for the current of the whole system, instead in a traditional P.S. the power factor depends on the power factor of the load but is not very often good.
3) The dimensions ( overall for powers more than 500 W ) are smaller than the traditional P.S. and also the weight.
4) The heat generation is smaller ( say less than 50 % ) respect to a traditional P.S.
5) The cost ( if foreseen to produce more than 1000 pieces ) is lower than a traditional P.S.
6) If necessary you can easly extend the temperature range of the P.S.

Contra:
1) Usually the schematic is more complicated an for this reason more prone to problems with the delivery of the components necessary for the assembly
2) The switching is far more sensible for the surge existing on the mains ( ask to the owners of the modems ! )
3) The switching is more noisy respect to a traditional P.S. and for this reason i will not immagine to use it with a analog/digital converter with more than 16 bit.
4) due to the noise generated is much more difficult to respect the european normes for the electromagnetic compatibility ( EN50081 and EN50082 )
5) Being more components involved, in some projects the reliability is mouch lower than a traditional power supply
6) Due to the filtering necessary at the input EMC filter, the lekage current is usually higher than a normal power supply ( problem overall for the medical instrumentation )

Hope to have solved your problems
Bye

 

[GrimReaper]

Contradictions

Are not many.

1. Euro EMC standards can be met. EMC is highest in high current loop,
the switch, catch-diode, and LC filter. Keep this loop between these components as short as possible. Inductor must be shielded. You wont have any compliance problems.

2. Line surge's....use a transorb to protect your input. Should equal max
input voltage.

3. Input Capacitor is totally reactive at a frequency above 100k. The new
orange organic capacitors resolve leakage issues regarding medical issues.

4. Output Noise is a function of Ripple Current and ripple voltage.
Both can controlled with LC and approach a Linear reg output.

 

[GrimReaper]

See program SwitchercadIII In 20 Day

I have uploaded this Program for you.....Just install

 

[jodokus]

switched power supply generates less heath, uses less (battery) power but is more complex and needs measures against emc. Switchers are used when power is high to save energy and minimize cooling. Also when power is not so high but it comes from a battery. Linear supplies are used when battery life and heath are no issue, generally for low power non battery operated applications.